1. Field of the Invention
The present invention relates to an inkjet recording head which ejects ink from an orifice in the form of ink droplets, and an inkjet apparatus using the inkjet recording head. More particularly, the present invention relates to an inkjet recording head which ejects ink in a direction perpendicular to a substrate, is provided with heaters that are driven in a time-sharing fashion, and causes the ink to land on the proper location on the recording medium by shifting the position of the heater and the corresponding discharge opening, since the time-sharing driving causes the location where the ink lands to be shifted; and an inkjet apparatus using the inkjet recording head.
2. Description of the Related Art
An inkjet recording method, disclosed for example in Japanese Patent Laid-Open No. 54-51837, is different from other inkjet recording methods in that the action of thermal energy on ink is used as the driving force for discharging ink droplets. More specifically, in the recording method of the aforementioned disclosure, heating the ink produces air bubbles therein that form the ink into ink droplets that are discharged from an orifice (discharge opening) at the front end of the recording head and adhere onto a recording medium, whereby information is recorded on the recording medium.
In general, the recording head used in this recording method includes an ink discharge section, a heating resistor (heater), an upper protective layer, and a lower protective layer. The ink discharge section has an orifice for discharging ink, and an ink path communicating with the orifice and forming part of a heat-acting section, where thermal energy acts upon ink in order to discharge ink in the form of droplets. The heating resistor serves as an electrothermal conversion member that is a means which produces thermal energy. The upper protective layer protects the heater from ink, while the lower layer accumulates heat.
In order to take full advantage of the characteristics of the above-described head, it is necessary to use a larger number of heaters, which are disposed close together in a high-density arrangement for high-speed operation.
A larger number of heaters results in a larger number of electrical connections with an external wiring plate. In addition, when the heaters are disposed close together in a high-density arrangement, the pitch between the heater electrodes becomes smaller, which makes it impossible to make electrical connections using ordinary electrical connection methods, such as wire bonding.
In Japanese Patent Laid-Open No. 57-72867, this problem is overcome by forming a driving element on a substrate.
Japanese Patent Laid-Open No. 59-95154 discloses a recording head of the type that discharges ink in a direction perpendicular to a heat-acting portion surface by adhering an orifice plate to a substrate.
In general, when such a head has a large number of heaters, the heaters are driven in a time-sharing fashion in order to lower the peak voltage that occurs when all of the heaters are driven.
When the heaters are driven in a time-sharing fashion, however, a voltage is applied to heaters at different times, so that the discharge timing differs, causing ink to land on the recording paper in a zigzag fashion.
To overcome such a problem in the recording head of the above-described type, a proposal has been made to shift the positions of the heaters in accordance with the timing of the time-sharing driving.
FIG. 5 is a view showing the vicinity of the heaters 202-1 and 202-2 in a conventional recording head. As shown in FIG. 5, when the driving elements 205 are arranged side by side and a common electrode is formed on the driving elements, the resistance of a selection electrode varies with the position of the heater, since a shift in the heater position changes the separation distances between the heater and the driving element wiring.
In addition, since the distance between the heater and the common electrode changes, the resistance value of the wiring between the heater and the common electrode changes.
Further, the aforementioned pattern has the following two problems. The first problem is that the wirings, which pass between the heaters, get in the way when the heaters are disposed very close together in a high-density arrangement. In addition, it becomes difficult to operate the heaters at a high frequency, since they can be less freely arranged in the lateral direction. The second problem is that a folded electrode, provided between the heater and the ink supply opening 208, increases the distance between the heater and the ink supply opening and thus increases the flow resistance between the heater and the ink supply opening. This deteriorates the discharge frequency characteristics, so that discharge cannot be performed at a high frequency.
Accordingly, in order to overcome the above-described problem, a proposal was made to form the pattern without the folded electrodes between the heaters 202-1 and 202-2 and the ink supply opening 208, as shown in FIG. 6.
In such a pattern, however, shifting the heater position causes the distances between the heaters and the driving elements 205 to become different, as well as the distances between the heaters and the common electrode to be different, thereby causing the resistance values of the individual selection wirings of the heaters, as well as the resistance values of the wirings between the heaters to be different. Therefore, a different voltage is applied to the heaters, which results in poor printing performance. In the worst case, ink cannot be discharged, depending on the heater position.
Accordingly, with the pattern shown in FIG. 6, it is necessary to design the electrodes and the driving elements such that a fixed voltage is applied to the heaters, in accordance with their positions. In particular, it is necessary to give good consideration to the method of correcting the resistances, since the wiring resistances can only be corrected within a narrow space between the driving elements and the heaters, when forming a driving element to the substrate.
Accordingly, an object of the present invention is to provide an inkjet recording head which can provide a constant discharge performance, without variations in the print quality, by applying a fixed voltage to each of the shifted heaters. In the inkjet recording head, ink is discharged perpendicular to the substrate, and heaters that are driven in a time-sharing fashion are provided. The time-sharing driving causes the landing location of the ink on the recording medium to be shifted. Thus, the ink is made to land on the proper location by shifting the location of the heaters and the corresponding discharging openings.